The present invention relates to pressure sensors and door opening/closing monitoring systems, and more particularly to sensors suitable for detecting door opening/closing.
Various types of sensors for detecting opening/closing of doors are known including switch-type, optical-type and infrared type sensors. All of these sensors are subjected to a certain limitation; for example, they must be installed near a door to be detected, as they directly monitor a condition and a position of the door to be detected. In addition, as an installation of the sensor is readily noticeable by a third person, if it is employed in a security system for detecting an intruder, for example, a counter measure can be easily taken. Further, as only one door can be detected by one sensor, for the detection of opening/closing of a plurality of doors, a plurality of sensors corresponding to the number of the doors is required.
On the other hand, to solve the problem as described above, a sensor for detecting opening/closing of a door based on pressure change caused by the opening/closing of the door is disclosed in the publication of Japanese Utility Model Registration No. 3039782 entitled xe2x80x9cSensor for Automatic Security Systemxe2x80x9d, for example. In addition, Japanese Utility Model Registration No. 3039783 entitled xe2x80x9cAutomatic Security Systemxe2x80x9d discloses a system employing the same.
As shown in FIG. 1A, a sensor disclosed in these publications includes an opening 1a at one end of a cylindrical casing 1, a screen 3, an opposite electrode 4 and an amplifying circuit 5 arranged in this order from the side of opening 1a in casing 1 and acting as pressure receiving surfaces. Further, in a back side of casing 1, a partition wall 6 having a through hole 6a is arranged and a chamber 7 is formed between partition wall 6 and the back surface of casing 1, thus a differential-type fine differential pressure gauge is formed. The sensor senses with the pressure receiving surfaces a change in pressure in a space in which it is installed if there is a change and outputs a voltage as shown in FIG. 1B as a sensor output.
Thus, when, for example, the door is not opened nor closed and the pressure in the room is maintained at a constant level, the sensor output does not change (being maintained at a standard level), whereas when the door is opened or closed and the pressure in the room changes, the change in pressure in the room is reflected in a change in the sensor output, whereby the opening/closing of the door can be detected. In Japanese Utility Model Registration No. 3039783 xe2x80x9cAutomatic Security Systemxe2x80x9d, it is shown that the opening/closing of the door is monitored based mainly on an output from a differential-type fine differential pressure sensor, with one sensor as described above and one infrared sensor installed in the room.
The conventional sensor as described above (Japanese Utility Model Registration No. 3039782), however, is of a mechanical type and bulky. In addition, as an actual pressure change accompanying the opening/closing of the door is very small, a highly sensitive sensor is required. To increase the detectivity, a ratio of a depth L of casing 1 to a depth t of chamber 7 must be increased, which further increases the size and the shape of the sensor.
In addition, as the sensor is formed as a differential-type fine differential pressure gauge, the function is limited to the detection of the change in pressure and it cannot be known whether the change represents the opening or the closing of the door.
Further, according to the automatic security system, if there is a plurality of doors in the room, it is impossible to determine which door is opened. In addition, if the sensor itself has a trouble, the sensor output will be held at the standard level and determined to represent that there is no intruder. In other words, no function for detecting the failure of the sensor is provided. Thus various problems exist.
The present invention is made in view of the above described background and an object of the invention is to provide a pressure sensor and a door opening/closing monitoring system which will solve the problems as described above, is small and capable of detecting the opening/closing of the door with high sensitivity, allowing a detection of an operation condition, that is, whether the door is opened or closed, is subjected to less limitation in an installation position thereof and can be installed such that the sensor is not readily noticeable from outside, and allowing a determination on which door is opened/closed with a small number of sensors when a plurality of doors exists.
According to the present invention a pressure sensor is provided. The pressure sensor includes a pressure receiving side located in a gas; a reference pressure side located in the same gas as the pressure receiving side; a device for changing the speed of transmission of a change in pressure of the gas to said performance side. The pressure receiving side and the reference pressure side are subject to the same pressure during steady state conditions during which there is no gas flow.
In alternative embodiment of the present invention, a monitoring system for detecting the opening and closing of a door to a room is provided. The system includes a pressure sensor located in the room. The sensor includes a pressure receiving side located in a gas, a reference pressure side located in the same gas as the pressure receiving side, and a device for changing the pressure of the gas provided to the reference pressure side. The pressure sensor is configured to produce an output when the position of the door changes in response to a measured pressure difference between the reference pressure side and the pressure receiving side.
According to the present invention a monitoring system for determining which door among a plurality of doors in a room is opened or closed is provided. The system includes a plurality of pressure sensors positioned in the room; wherein each pressure sensor includes a pressure receiving side and a reference pressure side, both of the sides being exposed to the pressure in the room. Each pressure sensor includes a device for delaying the speed of transmission of a change in the pressure of the room to the reference pressure side. Each pressure sensor is configured to produce an output corresponding to a measured pressure difference between the pressure receiving side and the reference pressure side. The system further includes a means for determining which door opened or closed based on the difference between the production of outputs by each of said plurality of pressure sensors.
The present invention further includes a pressure sensing apparatus including a stem bonded to a cap to form a package. A sensor is positioned within the package. The sensor includes a reference pressure side and a received pressure side. The stem includes a first opening for supplying a gas to the received pressure side and the cap includes a second opening for supplying the gas to the reference pressure side. The apparatus further includes a device for changing the speed of transmission of a pressure change in the gas to the reference pressure side.
The present invention also includes a method of detecting the opening and closing of a door. The method may include the steps of positioning pressure sensors in a room containing the door, each of the sensors having a pressure receiving side and a reference pressure side, both of the sides being exposed to the pressure in the room; receiving a change in the pressure in the room associated with opening or closing the door on the pressure receiving side of each sensor; delaying the receipt of the pressure change on the reference pressure side of each sensor; measuring the pressure difference between the pressure receiving side and the reference pressure in each sensor; producing an output from each sensor corresponding to the measured pressure difference; and determining the position of the door based on the output.
A method of determining which door among a plurality of doors in a room is opened or closed is also provided. The method may include the steps of positioning a plurality of pressure sensors in the room, each of the sensors having a pressure receiving side and a reference pressure side, both of the sides being exposed to the pressure in the room; receiving a change in pressure in the room associated with opening or closing one of the plurality of doors on the pressure receiving side of each sensor; delaying the receipt of the pressure change on the reference pressure side of each sensor; measuring the pressure difference between the pressure receiving side and the reference pressure side of each sensor; producing an output from each sensor corresponding to the measured pressure difference; and determining which door among the plurality of doors was opened or closed based on comparing the output from each sensor.
To achieve the above described object, the pressure sensor according to the present invention is constructed as a pressure sensor detecting a pressure difference between a pressure receiving side and a reference pressure side in which a response to pressure is made different in the pressure receiving side and the reference pressure side. This pressure sensor is realized by a semiconductor pressure sensor including a diaphragm that is displaced according to a pressure, for example. Here, the pressure receiving side means a side to which a pressure to be measured is applied in a normal pressure sensor.
As the response to pressure is different from the pressure receiving side to the reference pressure side, if an abrupt pressure change at the opening/closing of the door is caused, for example, and the response (speed of response) is fast, the pressure change can be transmitted immediately to a pressure sensing unit of the pressure sensor, whereas if the response is slow, the pressure change will not be transmitted immediately. Hence, the transmission speeds of the abrupt pressure change at the pressure receiving side and the reference pressure side become different, and differential pressure is applied. Thus, the pressure change caused by the opening/closing of the door is represented as the differential pressure and detected by the pressure sensor.
On the other hand, when the pressure changes slowly as in the case of temperature change or atmospheric pressure change, the timings the change eventually reaches to the pressure sensing unit of the pressure sensor are same regardless of the difference in response and no differential pressure is produced. Thus, as the sensor output changes only in response to the abrupt change in pressure as in the case of opening/closing of the door, the opening/closing of the door can be readily detected.
In addition, by utilizing the difference in the speed of response to pressure, a small but highly sensitive sensor can be realized. In addition, the direction of pressure change is different in the case of door opening and in the case of door closing. In the present invention, as the differential pressure is detected, it can be determined whether the pressure increases or decreases. Thus, the opening/closing of the door, or more specifically, the operation condition of the door opening/closing can be known.
Further, as the change in pressure (differential pressure) is detected, the sensor is not necessarily installed near the door, which increase freedom in arrangement layout, and in addition, as the sensor does not directly monitor the operation of the door, it can be concealed behind a partition, a screen or the like. Further, the opening/closing of a plurality of doors can be detected by one sensor. If it is necessary to detect which one of the plurality of doors is opened/closed, a plurality of sensors must be provided.
Various means can be adopted as a device for changing the response to pressure. For example, the device can be a filter provided at least at the reference pressure side described above and acting as a resistance to a passage of a gas. The first embodiment realizes the device in this manner.
As another example of the device, a closed space-forming member (corresponding to a vessel 16 in the embodiment) provided at the side of the reference pressure can be employed. The closed space-forming member can be formed in a semiconductor forming a sensor or can be installed as an external attachment as in the embodiment. In addition, the closed space-forming member can be better realized when a minute hole is formed. The second embodiment realizes this. The formation of the closed space with the minute hole as described has an additional advantage, that is, clogging at the reference pressure side due to the dust and dirt can be suppressed as far as possible.
Here, by detecting the pressure in the room having a door at the pressure receiving side, and applying an equivalent pressure with the pressure in the room on the reference pressure side, a pressure variation accompanying the opening/closing of the door may be detected utilizing the difference in the response to pressure between the pressure receiving side and the reference pressure side. To apply the equivalent pressure to the pressure in the room on the reference pressure side, a pressure to the reference side can be introduced from outside the room, for example, if the pressure in the room is equal to the pressure outside the room. Of course, the pressure in the room may be applied to the reference pressure side as to the pressure receiving side. Here, xe2x80x9cequivalentxe2x80x9d is a concept covering xe2x80x9csamexe2x80x9d.
In the door opening/closing monitoring system according to the present invention, a plurality of pressure sensors provided with a device differing the response to pressure of the pressure receiving side and the reference pressure of the pressure receiving side and the reference pressure side for detecting the pressure difference between the pressure receiving side and the reference pressure side is prepared, and the plurality of pressure sensors is installed in a room with a plurality of doors to be monitored, and the system further includes a determination device (corresponding to an integrated determination unit 30 in the embodiment) determining which door is opened/closed based on a difference in sensor outputs from the plurality of pressure sensors.
Thus, with the use of the plurality of sensors, it can be determined which door is opened or closed. In other words, as the distance from the position of installation of each sensor to the door is different from each other, the time lag is produced between the arrivals of the transmitted pressure change caused by the opening/closing of the door to the installation positions of the sensors. Hence, by determining which sensor first detects the pressure change among the plurality of sensors, the door opened/closed can be identified. In addition, as the distance to a source of pressure change, that is, the opened/closed door can be known based on the time lag in detections at sensors, even if there are three doors as in the embodiment or more than three doors, it can be determined which door is opened/closed by installing at least two sensors.